Is Yu Wenchan the nephew of Emperor Wen of Sui Dynasty?

No. Jing Di Yuwen Chan's mother in the Northern Zhou Dynasty was Zhu Manyue, a great queen. Zhu Manyue is from the State of Wu. Because of his family's guilty conscience, he failed to enter the palace, and was assigned to the East Palace to be responsible for the clothing management of Prince Yu Wenyun. Later, when Yu Wenyun was lucky, he gave birth to his son Yu Wenchan.

Emperor Wendi of Sui Dynasty is the grandfather of Yuwen Eying, the half-sister of Yuwen Chan. Yuwen's mother is Yang Lihua, Tian Yuan Empress, Yuwen Yun, Northern Zhou Emperor Xuan Di, and Yang Lihua is the daughter of Emperor Wendi of Sui Dynasty. In the 11th year of Daye (6 15), because of the prophetic incident (the 11th year of Daye (6 15), Fang said that "liying was the son of heaven", and he persuaded the emperor to kill everyone surnamed Li in the world. Yu's husband, whose nickname is Honger, was given by his uncle Yang Guangci.